This proposal describes the development of portable, cost-effective, and energy-efficient chemical sensors for detection of carbon monoxide, formaldehyde, methanol, ethanol, acetone, and hydrogen. Sensing these volatile compounds could both prevent and diagnose health problems. Some diseases are attributed to exposure to low levels of a volatile compound. For instance, formaldehyde, a common indoor pollutant, has been correlated with asthma rates. On the other hand, the human body exhales a set of molecules containing diagnostic information on the health of the individual. For example, trained dogs can detect lung cancer by the smell of a person's breath. Cost-effective and low-powered gas sensors could be deployed in an always-on networked array to prevent exposure to harmful chemicals; portability could extend application of gas sensors to monitoring personal health, which could revolutionize breath vapor analysis in health care. Current sensor technologies are limited. While gas chromatography is the gold standard for accurately identifying trace compounds, the instrumentation is costly and requires specialized training to operate. Other platforms to detect volatiles (fuel cells, infrared spectroscopy, etc.) may be simpler to operate, but face problems with sensitivity, selectivity, cost, and power consumption. To tackle these issues, an electronic nose strategy has been explored in which an array of sensors is utilized in concert to determine the chemical fingerprint of a vapor sample. In particular, Swager and coworkers have investigated resistive sensors based on functionalized carbon nanotube networks, potentially leading to inexpensive, low-powered, robust, and portable chemical sensors. Further improvements in sensitivity and selectivity of these sensors could lead to commercially viable devices. The goal of this research is to make a network of single-walled carbon nanotubes connected by organometallic linkages. These linkages are designed to increase electronic communication between adjacent nanotubes and, thus, the overall resting conductivity. Select volatile compounds are expected to disrupt these organometallic centers via oxidation, reduction, or ligand substitution. The overall sensor should be more sensitive and selective than purely organic-functionalized or metal-functionalized nanotube networks. The ultimate goal of this work is to develop sensitive, portable, and always-on sensors to detect environmental VOC exposure at levels well below toxicity thresholds and to monitor breath vapor VOCs of patients to aid in diagnosis of diseases such as lung cancer.